Vortex flowmeter

ABSTRACT

A vortex flowmeter for measuring fluid flow includes a conduit having a wall surrounding a bore for carrying the fluid along a bore axis. A pivoting member moves in response to vortices in the fluid and extends from a hole in the wall into the bore, and sensing means is provided for sensing the motion of the pivoting member to provide a flow indicative output. In one embodiment, a torsional pin is disposed in the hole and couples to the pivoting member, and further has a first pin end attached to the wall. In another embodiment a diaphragm extending across the hole, together with the conduit wall and the pivoting member, are integrally formed from a material so as to present an unbroken overall surface to the fluid and to reduce crevices or gaps in which portions of the fluid can lodge. In another embodiment the pivoting member is at least a portion of a downstream extremity of a body disposed in the bore. The body includes, in addition to the downstream extremity, an upstream extremity and a thinned area which flexes to permit motion of the pivoting member. In still other embodiments, the conduit is eliminated and replaced by a seating ring adapted to mate with a port of a conduit.

This is a continuation of application Ser. No. 07/956,398, filed Oct. 5,1992, now U.S. Pat. No. 5,343,762.

BACKGROUND OF THE INVENTION

This invention relates to flowmeters, and in particular to flowmeterswhich operate on the principle of measuring the frequency or period ofvortices in a Karman vortex street set up in a moving fluid.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the present invention relates to a vortex flowmeterfor measuring fluid flow, which flowmeter includes a conduit having awall surrounding a bore which carries the fluid along a bore axis. Apivoting member extends from a hole in the wall into the bore, and atorsional pin having at least one pin end attached to the wall couplesto the pivoting member. The torsional pin has a pin axis substantiallyparallel to the bore axis to permit pivotal motion of the pivotingmember about the pin axis. The flowmeter includes sensing means coupledto the pivoting member for sensing its motion, in order to provide anoutput indicative of the flow. The torsional pin provides a restoringforce tending to force the pivoting member back to its equilibriumposition. Also, the pin reduces undesired motion of the pivoting memberabout axes perpendicular to the pin axis, while permitting motion aboutthe pin axis.

In a preferred embodiment, the flowmeter also includes a diaphragm orother region of reduced stiffness which covers or seals the wall hole.By arranging the torsional pin to reinforce the diaphragm, the pinenhances the measurement capability of the flowmeter by reducing effectsof fluctuating and static line pressure on the diaphragm.

In another preferred embodiment, the conduit is eliminated and replacedby a member, such as a seating ring, adapted to mate with a port in aconduit. The resulting flow device inserts into a conduit port in eithera removable or permanent fashion.

Another aspect of the invention relates to a vortex flowmeter formeasuring fluid flow, in which a conduit has a wall surrounding a borefor carrying the fluid, the wall having a region of reduced stiffness,preferably a diaphragm, formed therein. A pivoting member disposed inthe bore connects to the diaphragm, and sensing means couples to thepivoting member to sense pivotal motion thereof and to provide an outputas a function of the deflections. According to this aspect of theinvention, the wall, diaphragm, and pivoting member are integrallyformed from a material so as to present an unbroken overall surface tothe fluid and to reduce crevices or gaps in which portions of the fluidcan lodge. In a preferred embodiment, the sensing means detachablyconnects to a post which in turn connects to the pivoting means throughthe diaphragm, the post being integrally formed with the other flowmetercomponents.

Another aspect of the present invention relates to a vortex flowmeterfor measuring fluid flow, the flowmeter comprising a conduit having awall surrounding a bore for carrying the fluid, the wall having a wallregion of reduced stiffness, preferably a diaphragm, formed therein. Abody disposed in the bore has an upstream extremity, a downstreamextremity, and an intermediate portion connecting the upstream anddownstream extremities. In a preferred embodiment, the intermediateportion includes a body region of reduced stiffness which is preferablya thinned area. One of the extremities, preferably the downstreamextremity, has a first end connected to the wall region. The body regionflexes to promote motion of at least a portion of the downstreamextremity resulting from disturbances within the fluid induced by fluidflow around the body. The flowmeter further includes sensing meanscoupled to the downstream extremity for sensing the motion and providingan output as a function thereof and thereby also as a function of theflow. In another preferred embodiment, the downstream extremity has asecond end connected to the conduit wall, and the body includes a secondthinned area disposed between the first and second ends of thedownstream extremity, the second thinned area also flexing to promotethe motion. In still another preferred embodiment, the sensing meanspreferentially senses lateral motion rather than longitudinal motion,and removably attaches to a post extending from the wall region awayfrom the bore, the post transmitting the motion to the sensing means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are partial cut-away views of flowmeters in accordancewith the present invention;

FIG. 1c is a cross-sectional view of a pivoting member and someneighboring parts taken along line 1c--1c of FIG. 1b;

FIG. 2a is a view of the torsional pin of FIG. 1b with neighboringparts, viewed from above;

FIG. 2b is an overhead view of a torsional pin with neighboring parts,wherein the pivoting member is a complete shedding bar;

FIGS. 3a-3d are cross-sectional views of torsional pin and region ofreduced stiffness arrangements useable with the invention;

FIGS. 4a and 4b are partial cut-away views of further flowmeters inaccordance with the present invention;

FIG. 5a is a partial cut-away view of still another flowmeter inaccordance with the present invention;

FIG. 5b is a cross-sectional view along line 5b--5b in FIG. 5a;

FIGS. 6a and 6b are views of a flow module in accordance with thepresent invention;

FIG. 7a is a cross-sectional view of the shedding bar of FIG. 1b, takenalong line 7a--7a;

FIG. 7b is a cross-sectional view of a PRIOR ART shedding bar assembly;

FIG. 8 is a cross-sectional view taken along line 1c--1c in FIG. 1b;

FIGS. 9a, 9b, and 9c are views of a shedding bar with a cover memberuseable with the present invention;

FIGS. 10a and 10b are cross-sectional views of an alternate shedding barshape useable with the present invention; and

FIGS. 11a and 11b are cross-sectional views of still another sheddingbar shape useable with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1a, flowmeter 10 includes a conduit 12 having a wall 14surrounding a bore 16. Bore 16 carries a fluid, which can be a liquid ora gas, generally along a directed bore axis 18. As is known in the art,a Karman vortex street results when a fluid flows around an obstruction,provided the Reynolds number of the flow is in a specified range. InFIG. 1a, shedding bar 20 is the vortex-generating obstruction.Fluctuating fluidic pressures act on pivoting member 22, which extendsfrom a hole 24 formed in wall 14 into bore 16, and on other portions ofshedding bar 20, such that pivoting member 22 moves in response to thefluctuating pressures. According to an aspect of the invention, atorsional pin 26 is disposed in hole 24 and coupled to pivoting member22. One or, preferably, both pin ends 26a,26a are fixedly attached towall 14, and a pin axis 27 is substantially parallel to bore axis 18.With this arrangement, portions of pin 26 between fixed pin ends 26a,26atwist about pin axis 27 as shown by double arrow 30 in response topivotal motion of pivoting member 22 about pin axis 27, shown by doublearrow 32. Since pin ends 26a,26a are fixed to conduit wall 14, pin 26provides a force tending to restore pivoting member 22 to its equilbriumposition. Such restoring force tends to increase the natural frequencyof vibration of pivoting member 22, which is advantageous to ensure thatthe natural frequency of pivoting member 22 is higher than the highestvortex frequency to be encountered during operation. Pin 26 alsofunctions to reduce undesired motion of pivoting member 22 parallel tobore axis 18, which motion is normally caused by local mechanicalvibration or other influences not indicative of the fluid flow. Byreducing such motion, noise and spurious signals are thus reduced in theinstrument. Moreover, pin 26 permits flow-indicative motion of pivotingmember 22 transverse to the flow, shown at double arrow 32. Sensingmeans 34, coupled to pivoting member 22 preferably by attachment to apost 28, senses the motion of pivoting member 22 and provides an outputat 36 indicative of the motion and therefore also of the flow, since thefrequency of the motion is a function of the volumetric flow rate. Post28 pivots about pin axis 27, moving predominantly along double arrows38, due to the above described influence of pin 26 and pivoting member22.

In FIG. 1a, hole 24 is preferably sealed by known means such as a coveror cap, not shown, to reduce or prevent fluid leakage from bore 16through hole 24 to the environment around conduit 12. Also, shedding bar20 preferably has a general shape or outline predominantly as describedin U.S. Pat. No. 4,464,939, assigned to the same assignee as the presentapplication and incorporated herein by reference.

FIG. 1b shows a flowmeter 10a similar to flowmeter 10 except thatflowmeter 10a includes a region of reduced stiffness, shown in FIG. 1bas diaphragm 40, extending across hole 24. Diaphragm 40 thus borders onblind hole 24a, and preferably fluidically isolates hole 24a from bore16. By isolating sensing means 34 or other flowmeter components from themeasured fluid, flowmeter 10a can measure benign as well as harsh fluidssuch as acids.

In addition to the beneficial functions of torsional pin 26 mentioned inconnection with FIG. 1a, pin 26 can benefit flowmeter 10a further whenused to reinforce diaphragm 40. First, by reinforcing diaphragm 40, pin26 enhances measurement capability in the presence of changing linepressure of the fluid (line pressure being the pressure of the fluid inbore 16 referenced to the environment outside wall 14) when comparedwith a similar flowmeter without pin 26 used as a reinforcement. Nonzerovalues of line pressure produce stresses in and cause distortions ofdiaphragm 40. Changing line pressure accordingly changes those stressesand distortions, giving rise to motion of diaphragm 40, pivoting member22, and post 28. Preferred sensing means 34, discussed in more detailbelow, preferentially senses transverse motions of post 28 rather thanlongitudinal motions of post 28 along its length. With such sensingmeans, benefits can be realized by making the effective area of bothhalves of diaphragm 40 approximately equal (the halves being separatedby pin 26), and by precisely positioning or centering the pivotingmember on the diaphragm, so that changes in line pressure causepredominantly longitudinal rather than transverse pivotal motion of post28. In practice, however, sensing means 34 does, to some extent, sensemotion of post 28 and the other members due to changing line pressure.If the line pressure fluctuates in a periodic fashion, caused forexample by a mechanical pump in the flow stream, then the correspondingmotion of diaphragm 40, pivoting member 22, and post 28 can be detectedby sensing means 34 and erroneously interpreted as a flow signal. Byreinforcing diaphragm 40, pin 26 reduces the stresses and distortionsdue to line pressure effects, thereby reducing the accompanying motionof the post and other flowmeter components, and enhancing measurementcapability.

Second, by strengthening diaphragm 40 pin 26 raises the value of linepressure needed to rupture diaphragm 40, thereby permitting higherstatic line pressure operation. Both pin ends 26a,26a are preferablyattached directly to conduit wall 14 for maximum strengthening andreinforcement of diaphragm 40.

FIG. 1c depicts the vicinity of diaphragm 40 of FIG. 1b in cross-sectionalong line 1c-1c, and illustrates (in greatly exaggerated fashion) thepivotal motion of member 22, the twisting of torsional pin 26, and theflexing of diaphragm 40. Double arrow 32 indicates generally the motionof pivoting member 22. Solid line and broken lines show the position ofthe parts at maximum deflection in either direction.

The overhead view of FIG. 2a shows selected parts of flowmeter 10a asviewed from sensing means 34. Diaphragm 40 along with attached pivotingmember 22 advantageously form a rigid center diaphragm, having an outer(diaphragm) diameter determined by diameter 42 of diaphragm 40, and aninner (rigid center) diameter determined by effective diameter 44 ofpivoting member 22. In this context, in the case of a "center" made ofthe same substance as the diaphragm, a rigid center is a center having athickness generally at least six times the diaphragm thickness. Thepivoting member of this and other embodiments preferably rigidlyattaches to the diaphragm, thus forming a rigid center diaphragm, sothat forces acting on the pivoting member are efficiently transmitted tothe sensing means. In FIG. 2a, torsional pin ends 26a,26a are shownfixedly attached to conduit wall 14.

FIG. 2b shows a view similar to that of FIG. 2a, but wherein theflowmeter differs somewhat from that of FIGS. 1a and 1b. In FIG. 2b,pivoting member 20a is substantially a complete shedding bar, comprisingupstream extremity 104, intermediate portion 106, and downstreamextremity 108. Torsional pin 26b has pin ends 26c,26c fixedly attachedto conduit wall 14. Pivoting member 20a has an effective diameter 44a,and diaphragm 40 has a diaphragm diameter 42a. FIG. 2b also shows post28. Alternately, to permit greater motion of pivoting member 20a whilemaintaining a rigid connection to diaphragm 40, portions of pivotingmember 20a adjacent to diaphragm 40 and extending beyond the perimeterof post 28 can be undercut. In such case, the diameter of the rigidcenter can have a value between the diameter of post 28 and diameter44a. If undercutting is employed at the attachment of the pivotingmember to the diaphragm, the lateral width of the undercut portionshould be at least 50% of the lateral width of the pivoting member end,to maintain a rigid connection. "Lateral width", in FIG. 2b, means thewidth measured along an axis in the plane of the figure butperpendicular to axis 27.

FIGS. 3a-3d show cross-sectional views of some more diaphragm andtorsional pin configurations useable with the invention. In FIG. 3a,diaphragm 40a has a shape which is flat, and is joined to pivotingmember 22. In FIG. 3b diaphragm 40b has a shape which is curved toconform to the generally right circular cylindrical shape of bore 16. Acurved diaphragm has increased stiffness relative to a flat diaphragm,thereby reducing sensitivity of the flowmeter for a given diaphragmthickness. For a given minimum sensitivity, therefore, a flat diaphragmcan have a greater thickness than a curved one, which is generallybeneficial if the diaphragm is to be integrally formed. Curveddiaphragms, on the other hand, improve flow characteristics of the fluidby conforming to the curved shape of pipe surfaces, and can be easier tofabricate than flat ones when using integral forming techniques. In FIG.3c region of reduced stiffness 40c completely fills the hole in wall 14.Further, region 40c covers torsional pin 26d. Region 40c is composed ofa substance having a reduced intrinsic stiffness with respect to conduitwall 14 adjacent to region 40c. Pin 26d is shown imbedded in region ofreduced stiffness 40c, the pin being composed of a substance havingincreased intrinsic stiffness with respect to region 40c. Finally, FIG.3d shows diaphragm 40d disposed near the outer surface of conduit wall14 rather than near the inner surface proximate the bore. In sucharrangement blind hole 24b is disposed on the same side of the region ofreduced stiffness as bore 16, in contrast to the hole arrangement inFIGS. 3a and 3b.

Flowmeters 10 and 10a in FIGS. 1a and 1b can use many types of sensingmeans 34 to sense the motion of pivoting member 22. As an example,sensing means can employ known optical techniques to detect deflectionsof pin 26, post 28, or diaphragm 40 caused by the motion of pivotingmember 22. In a preferred embodiment, flowmeters 10 and 10a include post28 extending from torsional pin 26 or diaphragm 40, and sensing means 34is a removeable or replaceable module coupling to post 28 and utilizingpiezoelectric discs or crystals. This preferred sensing means includesan axially flexible diaphragm transmitting side-to-side (lateral)motions of post 28 to the piezoelectric crystals, but flexing so as tosuppress transmission of motions along the length of post 28 to thepiezoelectric crystals. The preferred sensing means is described in U.S.Pat. No. 4,926,695, assigned to the same assignee as the presentapplication and herein incorporated by reference. The ability of thesensing means to preferentially sense lateral rather than longitudinalmotion is important to ensure that the flowmeter will operatesatisfactorily under nonideal operating conditions. Also, it isimportant that the preferred sensing means does not press against, load,or otherwise restrict diaphragm 40, thereby to permit diaphragm 40 tofreely flex.

FIG. 4a shows a flowmeter 10b similar to the flowmeter of FIG. 1a, withconduit wall 14a surrounding bore 16a, and having pivoting member 22bcoupled to torsional pin 26. FIG. 4b shows a flowmeter 10c similar tothe flowmeter of FIG. 4a, but additionally having a diaphragm 40eextending across the hole in conduit wall 14a. Diaphragm 40e acts as aregion of reduced stiffness within conduit wall 14a.

FIG. 5a shows, in partial cut-away view, a further embodiment 10d of aflowmeter utilizing the torsional pin of the present invention. Fluidflows generally along directed bore axis 18 around a portion ofobstruction 42 disposed in bore 16b, referred to as a shedding barportion, setting up a Karman vortex street in the fluid. Obstruction 42,coupled to torsional pin 44 and preferably also to post 46, pivots orbends generally about pin axis 48 in response to fluidic disturbancesassociated with the vortices. Obstruction 42 also pivots or bends aboutaxis 49 (shown in FIG. 5b) proximate its other end. The ends oftorsional pin 44 are integrally joined to seating ring 50, which in turnattaches via a weld joint 51,51 around its periphery to conduit wall14b. The pin ends are thereby fixedly attached to conduit wall 14b sothat flowmeter 10d benefits from the torsional effects of the pin,discussed previously. Sensing means 34 senses motion of obstruction 42via post 46 and provides output 36 as a function of such deflections.Flowmeter 10d also preferably includes diaphragm 52 extending acrossseating ring 50 such that pin 44 reinforces the diaphragm.

A flow module comprising obstruction 42, pin 44, and seating ring 50 canserve as a flowmeter when coupled to sensing means 34 and inserted intoconduit 14b. Such a flow module, also preferably including diaphragm 52and post 46, inserts into and mates with port 54 of conduit wall 14b. Tohold the flow module in place, other known methods besides welding canbe used to secure seating ring 50 to conduit 14b, such as brazing,cementing, solvent bonding, press-fitting, screwing, and so on.

FIG. 5b shows a partially broken away sectional view taken along line5b,5b of FIG. 5a. To enhance pivotal motion, obstruction 42 can beundercut at a first end 53a where it couples to seating ring 50, and ata second end 53b where it couples to a lower seating member 56. Weldjoint 57a,57a secures obstruction 42 to lower seating member 56, andweld joint 57b,57b secures member 56 to conduit wall 14b. End 53apreferably has a circular cross-sectional shape having a diameter notless than a diameter of post 46. As discussed in connection with FIGS.2a and 2b, the undercut should be such as to maintain a rigid connectionbetween obstruction 42 and diaphragm 52. End 53b preferably has across-sectional shape which is elongated parallel to bore axis 18. Theundercut portions of obstruction 42 are disposed outside of bore 16b sothat they do not significantly affect the fluid flow. However,obstruction 42 is shaped such that small gaps, shown exaggerated at 58,remain between obstruction 42 and conduit wall 14b, thereby to allowpivotal motion of obstruction 42. Pivoting members shown in otherembodiments can also include an undercut region or regions to promotepivotal motion.

Also shown in FIG. 5b is a portion of a preferred sensing means 34a,including motion transmitting tube 34b and axially flexible diaphragm34c. Axially flexible diaphragm 34c is rigid in the lateral direction,efficiently transmitting forces to piezoelectric crystals (not shown),and weak in the axial direction so that vertical motions of post 46 arelargely absorbed by flexing of the axially flexible diaphragm 34c. Thesensing means does not press against or restrict diaphragm 52, allowingthe diaphragm 52 to freely flex.

FIG. 6a shows a partial cross-sectional side view of a removeable flowmodule 55 in accordance with the invention. FIG. 6b shows a view alongline 6b,6b. Flow module 55 is similar to flowmeter 10a of FIG. 1b,except that flow module 55 preferably does not include a conduit portionbut rather inserts into a port 60 of an existing conduit or pipe 62.Flow module 55 comprises seating ring 64, diaphragm 40, torsional pin 26having pin ends 26a,26a fixedly attached to seating ring 64, sheddingbar 20 of which pivoting member 22 is at least a portion, and preferablyalso module end 66 and post 28. The flow module is preferably integrallyformed from a material to reduce cost. Upon insertion of flow module 55into port 60, seating member 64 mates with port 60 and is secured toconduit 62 by screws 68a,68b,68c,68d. O-ring 70 effectively seals port60 to prevent fluid leakage out of conduit 62. Stiff ring clip 72, orother stiff attachment means, holds module end 66 firmly to conduit 62.In place of shedding bar 20 with pivoting member 22, flow module 55 caninclude other arrangements such as shedding bar 20b with pivoting member22b (FIG. 4a), or combined pivoting member and shedding bar 20a (FIG.2b), or obstruction 42 (FIGS. 5a and 5b). Sensing means 34 provides aflow-indicative output 36 as in previously discussed embodiments.

In embodiments of the invention utilizing both a diaphragm and atorsional pin, the pin is preferably disposed on a side of the diaphragmaway from the conduit bore, so as to minimally disturb fluid flow in thebore.

Another aspect of the present invention lies in the use of a "tail"portion of the shedding bar as a vibrating or pivoting member. Turningagain to FIG. 1b, shedding bar 20 comprises generally upstream extremity104a, intermediate portion 106a, and downstream extremity 108a.Downstream extremity 108a includes pivoting member 22, the motion ofwhich is sensed to provide output 36. Using the downstream extremity (ora portion thereof) as the pivoting member takes advantage of the factthat one edge--the trailing edge--is already free to pivotally deflectsince it is unattached except possibly at conduit wall 14. Additionally,the thinned area at 110, part of intermediate portion 106a, permitsgreater freedom of movement of the other edge--the leading edge--ofpivoting member 22 by bending or flexing. For efficient pivotal motion,the pivoting member is preferably a relatively stiff, rod-likestructure, it is exposed to the flowing fluid, and it rigidly attachesto the diaphragm formed in the conduit wall.

FIG. 7a shows a cross-sectional view, taken along line 7a--7a of FIG.1b, of shedding bar 20 which includes downstream extremity pivotingmember 22, thinned area 110, and upstream extremity 104a. The fluidmoves in the general direction shown by arrow 111. Broken circle 116shows the location of diaphragm 40. Disturbances induced by fluid flowaround shedding bar 20 produce alternating differential pressure acrossshedding bar 20. Arrows 114 represent differential pressure forcesacting on portions of the shedding bar at an instant in time, whichforces contribute to the motion of pivoting member 22.

Utilization of downstream extremity pivoting member 22 with thinned area110 has the advantage of increased surface area over which thedifferential pressure forces contributing to the motion act, whencompared to a similar size prior art shedding bar assembly 20c of FIG.7b. In that figure, arrows 114a show forces due to differential pressurewhich contribute to the motion of sensing beam 118, acting primarily atthe intermediate portion of shedding bar assembly 20c. Prior artassembly 20c is disclosed in U.S. Pat. No. 4,926,695, mentioned above.In FIG. 7a, forces at 114 act on pivoting member 22 and on thinned area110, producing a bending moment 120 about axis 122, perpendicular to theplane of FIG. 7a. The use of a relatively large surface area of sheddingbar assembly 20 enables thinned area 110 to be thicker than sensingdiaphragm 124 of FIG. 7b for a given measurement sensitivity. This isparticularly advantageous when shedding bar assembly 20 is integrallycast from a metal because known casting methods can reliably and at areasonable cost produce parts only if the thickness of such partsexceeds a given minimum thickness. For typical metals, flowmeter sizes,and sensitivity requirements the thickness of thinned area 110 isgreater than such minimum thickness, enabling integral castconstruction, while the thickness of prior art sensing diaphragm 124 isless than such minimum thickness, requiring individual machining ofparts. If desired, the natural frequency of pivoting member 22 can bespecified by adjusting or setting the thickness of thinned area 110, thefrequency increasing with increasing thickness.

By utilizing downstream extremity pivoting member 22 shedding bar 20 hasthe additional advantage over shedding bar assembly 20c of compatibilitywith a larger diameter diaphragm as shown by outline 116, compared withdiaphragm outline 115 for assembly 20c. Use of a larger diameterdiaphragm permits an increased diaphragm thickness while maintainingadequate diaphragm flexibility. This is advantageous for integrallyformed diaphragms for the same reasons discussed in connection with anintegrally cast thinned area 110.

Turning again to FIG. 1b, shedding bar 20 preferably also includesthinned area 112 as part of downstream extremity 108a. As shown, areas112 and 110 preferably meet to form an L-shaped feature. Across-sectional view taken along line 1c--1c appears in FIG. 8. There,arrows 126 similar to arrows 114 of FIG. 7a show forces due todifferential pressure which contribute to the motion of pivoting member22, such forces producing bending moment 128 about pin axis 27. Thinnedarea 112 flexes to promote pivoting of pivoting member 22 about axis 27.As with area 110, the thickness of area 112 can be adjusted or set toensure a sufficiently high natural frequency of pivoting member 22,while still ensuring adequate deflection measurable by sensing means 34.

One or both of the thinned areas 110, 112, if desired, can be eliminatedand replaced by material which is not "thinned" but rather conforms tothe shape of the unmodified shedding bar and which has reduced intrinsicstiffness compared to neighboring parts, thereby having increasedflexibility similar to the thinned areas in order to promote motion ofthe pivoting member. This approach is advantageous because it minimallyperturbs the relationship between the vortex-shedding frequency and theflow rate, since that relationship can change with modifications to theshape of the shedding bar outer surface such as by introduction ofthinned areas.

Alternately, reduced perturbation of the relationship between vortexfrequency and flow rate can be achieved by positioning a cover member ormembers over at least a portion of the thinned area. FIGS. 9a, 9b, and9c show a side, rear, and cross-sectional view, respectively, of such acover member 74 attached to shedding bar 20 of FIG. 1b. Weld points at76 hold cover member 74 in place. Cover member 74 substantially coversthinned area 112 such that downstream extremity 108a together with covermember 70 present a substantially uniform outer surface to the fluidalong the entire length of downstream extremity 108a. Gaps 78 betweencover member 74 and neighboring parts permit thinned areas 110 and 112to flex to substantially the same degree they could flex without thecover member, so as not to further restrict pivotal motion of pivotingmember 22. If desired, a cover member can also cover thinned area 110such that intermediate portion 106a together with that cover membersimilarly present a substantially uniform outer surface to the fluidalong its length.

FIG. 1a shows shedding bar 20 utilizing downstream extremity pivotingmember 22, as in FIG. 1b. FIG. 4a shows a shedding bar 20b, similar tothat of FIGS. 1a and 1b, which includes upstream extremity 104b,intermediate portion 106b (including thinned area 110a), and downstreamextremity 108b (including thinned area 112a). In FIG. 4a, however,thinned areas 112a and 110a attach directly to conduit wall 14a.

An alternative, though not preferred, embodiment of the inventionutilizes at least a portion of the upstream extremity rather than thedownstream extremity as the pivoting member. The differential pressureforces referred to earlier are believed to be generally weaker at theupstream extremity than at the downstream extremity, but may nonethelessbe sufficient when combined with the forces on the intermediate portionto yield a measurable motion of the upstream extremity. Like thedownstream extremity, the upstream extremity has an unattached edgewhich is free to deflect. Since the shape of the upstream extremity hasa particularly strong influence on the vortex shedding behavior of thedevice, incorporation of a thinned area in the upstream extremity tofacilitate pivotal motion of a portion thereof may adversely affect therelationship between vortex shedding frequency and flow rate. Thisproblem can be reduced either by using, in place of the thinned areas,material which conforms to the shape of the remainder of the sheddingbar and which has reduced intrinsic stiffness (referred to above), or byusing cover members with the thinned areas.

FIG. 10a shows in cross-section an alternate shedding bar shape useablewith the invention, the shedding bar 80 including upstream extremity 82,intermediate portion 84, and downstream extremity 86. FIG. 10b showsshedding bar 80 of FIG. 10a, but where intermediate portion 84 includesa thinned area 81 to promote pivotal motion of the downstream (orupstream) extremity. Similarly, shedding bar 90, shown in cross sectionin FIG. 11a and including upstream extremity 92, intermediate portion94, and downstream extremity 96, is also useable with the invention.FIG. 11b shows shedding bar 90 of FIG. 11a, but including thinned area91 as part of intermediate portion 94 to facilitate motion of thedownstream (or upstream) extremity.

Still another aspect of the present invention relates to the way inwhich parts of the flowmeter are formed and are held together. Inflowmeter 10 of FIG. 1a, conduit wall 14, shedding bar 20 (includingpivoting member 22 and thinned areas 110 and 112, labelled in FIG. 1b),torsional pin 26, and post 28 are preferably integrally formed from agiven material such as metal, plastic, ceramic, or the like. Investmentcasting from a metal such as a stainless steel, a carbon steel, or achromium-nickel alloy (e.g., Hastelloy, sold by Union Carbide Corp.) ispreferred for most flowmeters designed for industrial applications. Insimilar fashion, injection molding from plastic can be used in otherapplications. In flowmeter 10a of FIG. 1b, diaphragm 40 is integrallyformed with the parts referred to in connection with flowmeter 10. Suchan integrally formed flowmeter 10a has both cost benefits, by reducedmachining and assembly steps required for manufacture, and otherbenefits related to the absence of weld joints which are susceptible tocorrosion, and the absence of gaps or crevices between the parts inwhich the fluid can lodge. This latter feature is a result of thecontinuous unbroken overall surface to which the fluid is exposed,resulting from the integral forming process, and is required in sanitaryapplications in which the fluid is, for example, a food or beverage. Thepivoting member, torsional pin, diaphragm, and conduit wall shown ineach of FIGS. 1c, 2a, 2b, 3a, 3b, and 3d, as well as the post shown insome of the embodiments, are preferably integrally formed as a singleunit. Flowmeters 10b and 10c of FIGS. 4a and 4b (excluding sensing means34 with output 36) are also preferably integrally formed as singleunits. Flow module 55 of FIGS. 6a and 6b is also preferably integrallyformed. It is particularly advantageous to integrally form thediaphragm, as well as the thinned areas (shown for example at 110 and112 of FIG. 1b), along with the other parts because the diaphragm andthinned areas would require special care and cost in machining. Also,since the precise placement of the pivoting member on the diaphragm cangreatly affect the instrument's response to changing line pressure, byintegrally forming the diaphragm together with the pivoting member in apredetermined positional relationship, reduced sensitivity to changingline pressure can be assured in a highly repeatable fashion with littleor no assembly and at low cost.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A vortex flowmeter for measuring the flow of afluid, comprising:a conduit having a wall surrounding a bore forcarrying the fluid, the wall having a diaphragm integral with the wall;a pivoting member disposed in the bore and integral with the diaphragm;and sensing means coupled to the pivoting member for sensing pivotalmotion thereof and providing an output as a function of the pivotalmotion; wherein the wall, the diaphragm, and the pivoting member areintegral such that they present an unbroken overall surface to thefluid.
 2. The flowmeter as recited in claim 1, further including:a bodydisposed in the bore and including at least a portion of the pivotingmember; wherein the body induces disturbances in the fluid as a functionof the flow which cause the pivoting member to pivot with a frequencyindicative of the flow.
 3. The flowmeter as recited in claim 1, whereinthe conduit has a hole isolated from the fluid by the diaphragm.
 4. Theflowmeter of claim 1 wherein the material is a metal.
 5. The flowmeterof claim 4 wherein the metal is selected from the group consisting ofstainless steel, carbon steel, and chromium-nickel alloy.
 6. Theflowmeter of claim 1 wherein the material is a plastic.
 7. A vortexflowmeter for measuring fluid flow, comprising:a conduit having a wallsurrounding a bore for carrying the fluid, the wall having a integralwall region of reduced stiffness: a body disposed in the bore and havinga first and second extremity, the second extremity having a first endabutting the wall region, the first extremity being disposed so as tonot abut the wall region, the body further including a body region ofreduced stiffness; and sensing means coupled to the second extremity forsensing motion of at least a portion thereof resulting from disturbanceswithin the fluid, and providing an output as a function of the motionand thereby also as a function of the flow; wherein the body regionflexes to promote the motion and the fluid flow around the body inducesthe disturbances within the fluid.
 8. The flowmeter as recited in claim7, wherein the first extremity is an upstream extremity and the secondextremity is a downstream extremity.
 9. The flowmeter as recited inclaim 7, wherein the body region is a thinned area of the body.
 10. Theflowmeter as recited in claim 9, wherein the thinned area is disposedbetween the upstream and downstream extremities.